President Mohamed Morsi refused to quit hours before an army ultimatum expires on Wednesday as deadly violence rocked Cairo during mass protests demanding he resign, in Egypt's worst crisis since its 2011 revolution.
In a televised address early Wednesday, the embattled Islamist leader said he had been freely elected to lead the troubled nation little more than a year ago and intended to stick to his task.
The only alternative to respecting the constitutional legitimacy of the office was further bloodshed on the streets, he warned, adding that he stood ready to "give my life" to defend constitutional legitimacy.
Only hours after Morsi's speech, the health ministry reported that unidentified gunmen had killed 16 people and wounded about 200 more after opening fire on a rally by his supporters in Cairo.
With a showdown looming between Morsi and the army, Egypt's military chiefs said Wednesday they were ready to die to defend the people of Egypt.
"The general commander of the armed forces said it was more honourable for us to die than to have the people of Egypt terrorised or threatened," said a statement called "The Final Hours" posted on a page associated with the army.
"We swear to God that we will sacrifice our blood for Egypt and its people against all terrorists, extremists and ignorant" groups, it said, citing army chief Abdel Fattah al-Sisi.
Morsi's defiant speech came as the clock ticked down on a deadline set by the powerful military for him to meet the "people's demands" by 4:30 pm (1430 GMT) on Wednesday or have a solution imposed on him.
While he made no direct reference to the ultimatum in his speech, a message posted on his official Twitter account called on the army to back off.
"President Morsi insists on (his) constitutional legitimacy and rejects any attempt to overstep it," the message said.
"(He) calls on the armed forces to withdraw their warning and rejects any dictates, domestic or foreign."
But Egypt's state-owned and independent press predicted Wednesday would be the day of Morsi's departure.
"Today: Ouster or Resignation," read the front-page headline of the state-owned mass circulation daily Al-Ahram. "The End," declared the independent daily Al-Watan.
Cairo's streets were again unusually quiet on Wednesday, with many choosing to stay home over fears of more violence.
"The Islamists declared war on the rest of the population yesterday. I'm very scared," said Cairo resident Soha Abdelrahman.
In the neighbourhood of Giza, a group of men stopped a minibus carrying commuters, threatening to "kill anyone with a beard" in reference to Islamists, one witness told AFP.
After Morsi's speech, the opposition Tamarod movement, which on Sunday mobilised millions of demonstrators for what the military described as the biggest protests in Egyptian history, accused Morsi of "threatening his own people".
Morsi and General Sisi held talks on Tuesday to "discuss the current crisis," a military source said.
The army's 48-hour ultimatum drew a rapturous welcome from opponents of Morsi when it was delivered on Monday.
But his supporters accused the generals of preparing a return to the unpopular military rule of the months between the overthrow of former president Hosni Mubarak in February 2011 and Morsi's swearing-in on June 30 last year.
Government daily Al-Ahram, in its online edition, reported details of the demands set out by the army.
The army told Morsi to step down if he could not come up with a plan that would satisfy the masses calling for him to go, or face being removed, it reported.
The plan provided for an interim administration of up to a year to replace him, which would include the head of the supreme constitutional court and a senior army figure, the paper reported.
The constitution, controversially approved by Morsi's Islamist allies in December, would be suspended for up to a year while a new one was drawn up.
There would be presidential and legislative elections under terms set by the new constitution, which itself would be put to a referendum.
In addition to the 16 deaths at the pro-Morsi rally, seven other people were killed and dozens more injured in clashes Tuesday in the capital between the president's supporters and opponents.
Morsi's opponents accuse him of having betrayed the revolution by concentrating power in Islamist hands and of sending the economy into freefall.
His supporters say he inherited many problems from a corrupt regime, and that he should be allowed to complete his term, which runs until 2016.